Self-priming centrifugal pump

ABSTRACT

A self-priming centrifugal pump has enhanced efficiency and performance characteristics and/or features which facilitate installation, inspection and maintenance of the pump. For efficiency and performance, the pump may include a smooth fluid flow path which enhances pump output for a given input power, including one or more of a specially shaped and directed volute discharge, a lack of internal stiffening ribs on the pump casing walls, a necked inlet and a rounded, flow-channeling outlet aperture. For maintenance and serviceability, the pump may include one or more of a coarse-threaded drive shaft and impeller with a concentricity feature, a combination port for both filling the casing and accessing the inlet flapper valve, and a drive disassembly system which facilitates attachment or removal of the drive system from the pump.

BACKGROUND

1. Technical Field

The present disclosure relates to pumps and, in particular, toself-priming pumps with enhanced performance, efficiency and/orserviceability.

2. Description of the Related Art

Self-priming centrifugal pumps generally include a spinning impellerpositioned inside an annular volute, which in turn is positioned withina pump casing. The volute forms an eye at the center where liquid entersthe pump and is directed into the center of the impeller. Rotation ofthe impeller accelerates the liquid outward to the perimeter of theimpeller where it is collected in the volute and discharged from thepump casing at an elevated pressure. As the liquid is driven outward bythe centrifugal force of the rotating impeller, a vacuum formed at theeye is used to draw source fluid through the inlet and into the pump.

In a “wet prime” type pump, a centrifugal pump is arranged in a casingdesigned to retain water when the pump is not operating. When the pumpis started, the impeller in the pump casing starts to mix the retainedwater with the air in the case. Inside the casing, a “P-trap” isutilized to allow the air to be expelled from of the pump cavity via thepump outlet, while the water remains available to the impeller. This airexpulsion continues until enough air has been removed from the pipingconnected to the pump suction inlet so that the impeller eye becomessubstantially flooded. This point, the pump achieves prime.

In such wet prime pumps, the pump casing may include a partition toseparate the suction (i.e., inlet) side from the pressure (i.e., outlet)side so that the air/water mixture discharges exclusively toward theoutlet side of the casing. In the outlet-side chamber of the casingduring the self-priming operation, air is expelled via the outlet and isprevented from flowing back into the inlet-side chamber by thepartition, while liquid water remains available to flow back to thesuction side around the submerged or partially submerged pump impeller.

Self-priming centrifugal pumps are employed in applications where thesource liquid may not be uniform. For example, so-called “trash pumps”may be self-priming centrifugal pumps in which solids suspended in thefluid are allowed to be cycled through the pump. Trash pumps are usedfor, e.g., wastewater treatment, lift stations for municipal sewage, andwaste handling for food processing plants.

SUMMARY

The present disclosure provides a self-priming centrifugal pump withenhanced efficiency and performance characteristics and/or featureswhich facilitate installation, inspection and maintenance of the pump.For efficiency and performance, the pump may include a smooth fluid flowpath which enhances pump output for a given input power, including oneor more of a specially shaped and directed volute discharge, a lack ofinternal stiffening ribs on the pump casing walls, a necked inlet and arounded, flow-channeling outlet aperture. For maintenance andserviceability, the pump may include one or more of a coarse-threadeddrive shaft and impeller with a concentricity feature, a combinationport for both filling the casing and accessing the inlet flapper valve,and a drive disassembly system which facilitates attachment or removalof the drive system from the pump. Any combination of the aforementionedfeatures may be utilized in accordance with the present disclosure.

In one form thereof, the present disclosure provides a centrifugal pumpincluding: a drive mechanism; an impeller drivingly connected to thedrive mechanism; a casing having an inlet and an outlet. The casingincludes: an inlet-side wall having an inlet aperture formed therein; anoutlet-side wall joined to the inlet-side wall to form a cavity withinthe casing, the outlet-side wall having an outlet aperture; a volutedisposed in the casing and in fluid communication with the inletaperture and the outlet aperture, the volute having a central openingsized to receive the impeller and a spiral-shaped fluid channel suchthat the fluid channel progresses radially outwardly toward a volutedischarge opening, the volute discharge opening defining a longitudinaldischarge axis which extends through the outlet aperture. The volute isadapted to receive fluid accelerated outwardly by the impeller, directthe fluid radially outwardly through the spiral-shaped fluid channel,and discharge the fluid along the longitudinal discharge axis toward theoutlet aperture.

In another form thereof, the present disclosure provides a centrifugalpump including: a drive mechanism; an impeller drivingly connected tothe drive mechanism; a flapper valve; a casing having an inlet and anoutlet. The casing includes: an inlet-side wall having an inlet apertureformed therein, the flapper valve positioned at the inlet aperture toadmit a flow of fluid into the casing via the inlet aperture whilepreventing a flow of fluid out of the casing via the inlet aperture; anoutlet-side wall joined to the inlet-side wall to form a cavity withinthe casing, the outlet-side wall having an outlet aperture; a partitionwall interposed between the inlet-side wall and the outlet-side wall toform an inlet pump chamber and an outlet pump chamber, the partitionwall having an inner drive aperture positioned to allow fluidcommunication between the inlet chamber and the outlet chamber via theinner drive aperture; a combination port formed in the casing near theflapper valve, the combination port sized and positioned to allow accessto the flapper valve by a maintenance person, and to allow fluid to beadded to the inlet pump chamber; and a fill vent formed through thecasing on an opposite side of the partition wall as the combinationport, such that the fill vent allows fluid communication between theoutlet pump chamber and the ambient environment, whereby liquid added tothe inlet pump chamber is allowed to flow to the outlet pump chamber viathe inner drive aperture while air contained in the outlet pump chambervents to atmosphere via the fill vent.

In yet another form thereof, the present disclosure provides acentrifugal pump including: a drive shaft having a first coarse threadand a first centering feature; an impeller drivingly connected to thedrive shaft, the impeller having a second coarse thread and a secondcentering feature, the second coarse thread engageable with the firstcoarse thread of the drive shaft to selectively rotatably fix the driveshaft to the impeller, and the second centering feature engageable withthe first centering feature to concentrically align the impeller withthe drive shaft.

In still another form thereof, the present disclosure provides acentrifugal pump comprising: a drive mechanism; an impeller drivinglyconnected to the drive mechanism; a casing having an inlet and anoutlet, and a drive disassembly system. The casing includes: aninlet-side wall having an inlet aperture formed therein; an outlet-sidewall joined to the inlet-side wall to form a cavity within the casing,the outlet-side wall having an outlet aperture; a bore extendinginwardly from the exterior of the outlet-side wall whereby the bore isaccessible to a user of the pump. The drive disassembly system includes:a guide rail sized to be snugly received within the bore of thestiffener; and a rail guide having a bearing and a flange fixed to thebearing, the bearing sized to be slidingly received on the guide railwhile the flange is fixed to the drive mechanism, such that the drivemechanism can be assembled into or removed from the casing while beingsupported by the guide rail.

In still another form thereof, the present disclosure provides a methodof disassembling a drive mechanism from a centrifugal pump, the methodincluding: inserting a rail into a bore formed in a casing of the pump,such that the rail fits snugly within the bore; sliding a rail guideover the rail and into engagement with the pump; affixing the rail guideto the drive mechanism while maintaining the rail guide in slidingengagement with the rail; and disconnecting the drive mechanism from thecasing and sliding the drive mechanism away from the casing using thesupport of the rail.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features of the disclosure, and the mannerof attaining them, will become more apparent and will be betterunderstood by reference to the following description of embodiments ofthe disclosure taken in conjunction with the accompanying drawings.These above-mentioned and other features of the invention may be used inany combination or permutation.

FIG. 1 is an elevation, cross-section view of a centrifugal pump made inaccordance with the present disclosure, taken along the line I-I of FIG.8 but with the drive disassembly system of FIG. 8 removed;

FIG. 2 is an enlarged view of a portion of FIG. 1, illustrating a driveshaft assembly connection to the pump impeller;

FIG. 3 is a perspective view of the pump shown in FIG. 1, illustrating aflapper access port and fill vent;

FIG. 3A is a perspective view of an alternative pump casing inaccordance with the present disclosure;

FIG. 3B is another perspective view of the alternative pump casing shownin FIG. 3A;

FIG. 4 is an elevation, cross-section view of the casing of the pumpshown in FIG. 1, taken along the line IV-IV of FIG. 1;

FIG. 5 is an elevation, cross-section view of the casing of the pumpshown in FIG. 1, taken along the line V-V of FIG. 4;

FIG. 6 is a bottom plan, cross-section view of the casing of the pumpshown in FIG. 1, taken along the line VI-VI of FIG. 1;

FIG. 7 is an elevation, partial cross-section view of the pump shown inFIG. 1, taken along the line VII-VII of FIG. 8, illustrating the pumpoutlet;

FIG. 8 is a perspective view of the pump shown in FIG. 1, and includinga drive disassembly system attached thereto;

FIG. 9 is another perspective view of the pump shown in FIG. 8,illustrating removal of the drive mechanism via the drive disassemblysystem;

FIG. 10 is a perspective view of the drive shaft and impeller shown inFIG. 1;

FIG. 11 is an exploded, partial cross-section view of the pump shown inFIG. 1, illustrating an impeller inspection port;

FIG. 12A is a perspective, cross-section view of the casing of the pumpshown in FIG. 1;

FIG. 12B is a perspective view of the pump shown in FIG. 1, illustratingfeatures on the inlet side of the pump; and

FIG. 13 illustrates centralizing single-start Acme threads.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate embodiments of the disclosure and such exemplifications arenot to be construed as limiting the scope of the invention in anymanner.

DETAILED DESCRIPTION

The present disclosure provides a self-priming centrifugal pump, shownas pump 10 in, e.g., FIGS. 1, 3 and 8, which includes various featuresproviding increased pump efficiency and/or facilitating installation,inspection and maintenance, among other benefits.

For example, as shown in FIG. 1 and further described in detail below,centrifugal pump 10 includes volute 34 having a geometry andconfiguration which tends to “aim” pressurized fluid toward outletaperture 20 to aid in efficient fluid discharge. Outlet aperture 20 hasa rounded, gradual transition area 102 leading to outlet adapter 98 tofurther facilitate discharge of pressurized fluid with minimal losses.Fastener bosses 104 are similarly rounded and shaped to minimize eddyingand turbulence in the vicinity of outlet aperture 20 and direct the flowefficiently through outlet aperture 20.

Further, both inlet pump chamber 30 and outlet pump chamber 32 aresubstantially free of stiffening ribs, which also promotes a smooth andlaminar fluid flow through chambers 30, 32 and minimizing turbulence.More particularly, inlet and outlet pump chambers 30, 32 are eachsubstantially defined by respective inner surfaces of casing 12, and byrespective surfaces of partition wall 24 as shown in FIG. 5 and furtherdescribed below. These surfaces are substantially free of stiffeningribs such that no stiffening ribs are disposed within the fluid flowpaths through chambers 30, 32. In order to provide strength to casing12, stiffening ribs 100 are located at the outside surface of the pumpcasing 12 as shown, e.g., in FIG. 3. An alternative design of stiffeningribs 100A is shown in FIGS. 3A and 3B.

Still further efficiency and performance is realized by locating drainplugs 130, 134 (FIGS. 11 and 12B, respectively) and their associateddrain channels 132 (FIG. 11) and 136 (FIG. 12A) at locations outside theflow path of volute 34, in order to provide for gravitationally drainingthe pump casing 12 without introducing any features in the vicinity ofvolute 34 which can cause turbulence or eddying and thereby mitigatingabrasive wear during pump operation.

With regard to serviceability, pump 10 includes combination port 82(FIG. 3) which doubles as a flapper access portion and a fill port foradding liquid (e.g., water) to casing 12 for pump priming. Fill vent 92facilitates this priming functionality, while combination port cover 84provides a single integral unit for covering both port 82 and vent 92.Combination port 82 both reduces manufacturing cost and complexity byrequiring only one aperture through casing 12 for two functions, whilealso facilitating installation and maintenance of pump 10 as describedbelow.

Pump 10 may also be used in conjunction with drive disassembly system 50(FIGS. 8 and 9) to facilitate removal of drive mechanism 40 from pumpcasing 12 for service or inspection. Reinstallation of drive mechanism40 is also made easier by drive disassembly system 50, as described indetail below.

Within drive mechanism 40, drive shaft 46 couples to impeller 44 viacoarse threads 72, 76 (FIG. 2), which promotes ease of installation andprevents cross-threading. In order to maintain a high level ofconcentricity between drive shaft 46 and impeller 44, the coarse threadsare supplemented with a tight-tolerance fit between distal nubbin 70formed on drive shaft 46 and bore 74 formed in impeller 44, as shown inFIG. 2.

Pump 10 further includes provisions for inspecting and maintainingimpeller 44 from the inlet side of casing 12, by removal of inspectioncover 110 and inspection side wear plate 112, as shown in FIG. 11.

Various features of centrifugal pump 10 are described in turn below. Theembodiment disclosed below is not intended to be exhaustive or limit theinvention to the precise forms disclosed in the following detaileddescription. Rather, the embodiment is chosen and described so thatothers skilled in the art may utilize its teachings. Moreover, it isappreciated that a pump made in accordance with the present disclosuremay include any one of the following features or any combination of thefollowing features, and may exclude any number of the following featuresas required or desired for a particular application.

1. Smoothed Interior Surfaces

Centrifugal pump 10 includes several features related to pump casing 12which, individually and in the aggregate, contribute to enhanced pumpefficiency and performance by minimizing turbulent flows and eddying offluid as it passes from inlet aperture 18 to outlet aperture 20 viainlet pump chamber 30 and outlet pump chamber 32.

For example, beginning at inlet aperture 18 shown in FIG. 1, inletadapter 90 may include a necked portion 91 with a gradually increasingflow area as fluid passes from inlet conduit 140 (FIG. 3) throughadapter 90 and toward inlet aperture 18 in casing 12. For example and asshown in FIG. 1, the flow area may substantially constant through acylindrical portion of adapter 90, and may then gradually increasethrough a tapered (e.g., frustoconical) necked portion 91 whichcontinuously increases the diameter of a circular flow area. Thiscontinuous and gradual increase provides a smooth, low-turbulence flowof fluid from inlet conduit 140 through inlet aperture 18 and into inletpump chamber 30, as necked portion 91 gradually relieves fluid pressureat inlet aperture 18 and allows fluid to more slowly and smoothlytransition its flow direction downward through pump chamber 30 towardimpeller 44.

Moreover, providing necked portion 91 in inlet adapter 90 allowscentrifugal pump 10 to be used with a variety of nominal sizes for inletconduit 140 and outlet conduit 142 (FIG. 3) for given sizes of inlet andoutlet apertures 18, 20. For example, adapters 90 and 98 may allow agiven size of centrifugal pump 10 (e.g., a 3-inch, 4-inch or 6-inchpump, referring to the nominal size of outlet conduit 142) to be usedwith various sizes of inlet and outlet conduits 140, 142 by providingthe appropriate set of adapters. For conduits 140 or 142 which do notmatch the size of apertures 18 or 20 respectively, a necked portion(e.g., necked portion 91) permits this size disparity while avoiding orminimizing a fluid efficiency penalty from an abrupt change in flow areafrom conduit 140, 142 and aperture 18, 20 respectively. It iscontemplated that either, both or neither of inlet and outlet adapters90, 98 may include a necked portion to facilitate smooth flow asrequired or desired for a particular application.

In an exemplary embodiment, inlet and outlet conduits 140 and 142 areprovided with the same nominal size while aperture 18 is larger thanaperture 20. Necked portion 91 provides a gradual “step up” of the flowpath area through inlet adapter 90 to accommodate an inlet fluid conduit140 of a smaller flow area than inlet aperture 18. At the same time,outlet adapter 98 may have a flow area substantially equal to outletaperture 20, in order to receive pressurized flow from volute 34 withoutposing an impediment to smooth flow. Outlet adapter 98 therefore may notneed a necked portion similar to necked portion 91 of inlet adapter 90.

After passing into inlet pump chamber 30, fluid is drawn into channels45 of impeller 44, which rotates under power provided by drive shaft 46to accelerate the fluid outwardly into fluid channel 36 of volute 34, asbest seen in FIGS. 4 and 5. In the illustrative embodiment of FIGS. 1,11, impeller 44 is a “double curvature” design including two fluidchannels 45 defining a fluid flow path which spirals radially outwardly.Although the illustrated design of impeller 44 is well suited to a“trash pump” application for centrifugal pump 10 (e.g., where pump 10accepts fluids with solids in suspension or other non-uniform fluidcharacteristics), it is appreciated that other designs may be used forimpeller 44 as required or desired for a particular application.

Pressurized fluid discharged from impeller 44 to volute 34 travelsthrough the spiral-shaped volute fluid channel 36 to discharge opening38, which defines discharge axis A_(V) “aimed” to pass directly throughoutlet aperture 20 as further described below. The pressurized fluid isdirected by discharge opening 38 along volute discharge axis A_(V), suchthat the fluid passes directly through outlet pump chamber 32 and towardoutlet aperture 20, as shown in FIGS. 4 and 5 and further described indetail below.

As the pressurized fluid approaches outlet aperture 20, outlettransition area 102 and fastener bosses 104 provide rounded and smoothtransition surfaces to facilitate smooth fluid flow from outlet pumpchamber 32 to outlet adapter 98 and ultimately to outlet conduit 142(FIG. 3). Specifically, referring to FIG. 5, the transition from thesubstantially horizontal top wall of outlet side wall 16 of casing 12 tothe substantially vertical side wall of outlet adapter 98 (i.e., the“internal edge” of outlet aperture 20) is a radiused (also known as“filleted”) transition in which the radius of the fillet is generallycommensurate with the thickness of the adjacent portion of outlet sidewall 16. In an exemplary embodiment, for example, the radius of thefillet varies from as little as equal to the minimum thickness of outletside wall 16 to as much as 1.3 the minimum thickness. In the illustratedembodiment, for example, the radius of the fillet around outlet aperture20 is 0.75 inches while the wall thickness is 0.57 inches, though ofcourse these nominal values will vary depending on the size and power ofpump 10. In exemplary embodiments, the nominal fillet radius is at least131% of the minimum wall thickness.

Fastener bosses 104 may be provided at the interior surfaces of casing12 (i.e., within inlet and/or outlet pump chambers 30, 32) adjacentinlet and/or outlet apertures 18, 20. Fastener bosses 104 provide forsufficient material to be available for threaded engagement of fasteners105 with casing 12 to connect adapters 90, 98 to inlet and outlet sidewalls 14, 16 respectively, as shown in FIG. 1. Referring to thedepiction of bosses 104 adjacent to outlet aperture 20 in FIGS. 5-7, itcan be seen that bosses 104 have a rounded profile which facilitatessmooth flow from outlet chamber 32 to outlet adapter 98 via outletaperture 20.

As best seen in FIGS. 1 and 7, fastener bosses 104 provide a smoothlyrounded, convex distal surface at their respective ends, and transitionto an annular concave surface which forms the junction between theconvex end surface and the adjacent inner surface of outlet side wall16. This concave-to-convex transition avoids abrupt corners or othersharp features within the fluid flow path in outlet chamber 32, andparticularly avoids such sharp features in the fluid flow path alongvolute discharge axis A_(V). In this way, rounded bosses 104 prevent orminimize turbulence in the fluid flow which might otherwise compromisepump efficiency and performance.

Although the lower-pressure space in inlet chamber 30 is lesssusceptible to adverse performance impacts relating to the shape ofbosses 104 around inlet aperture 18 or any other threaded aperture incasing 12, the same rounded shape of bosses 104 is provided for maximumpump efficiency.

Referring now to the bottom plan view of fastener bosses 104 in FIG. 6,three fastener bosses 104 closest to the volute discharge opening 38 areillustrated. In the context of FIG. 6, the three bosses 104 in questionare shown along right side portion of outlet aperture 20 and withinoutlet chamber 32. As illustrated, these bosses 104 are contoured in a“tear drop” shape, in which a pointed end of the tear drop is pointingtoward outlet aperture 20. This tear drop shape for fastener bosses 104promotes a substantially laminar flow over the outer surface of bosses104 as fluid discharged from volute 34 advances toward outlet aperture20.

Turning now to FIGS. 3 and 3A-3B, yet another flow-enhancing feature isillustrated in the form of exterior ribs 100 and 100A respectively,which are integrally and monolithically provided as a portion of theexterior of casings 12 and 12A respectively. Ribs 100 and 100A bothserve to strengthen and rigidify casing 12 in order to prevent orminimize any potential bulging or flexing of the material of casing 12from the substantial pressures (positive or negative) which may bedeveloped in pump chambers 30, 32.

In FIG. 3, a central vertical rib 100 extends from a lower base 106upwardly to outlet aperture 20 and outlet adapter 98 on either side ofcasing 12. For purposes of the present discussion, the “bottom” of pump10 is base 106 while outlet aperture 20 and adapter 98 is at the “top”of pump 10. “Vertical” is the direction extending from bottom to top. Inaddition, a plurality of front-to-back stiffening ribs 100 extend fromthe inlet side of casing 12, along inlet side wall 14, and terminate atthe central vertical rib 100. A further set of front-to back-ribs 100extend from the drive side of casing 12 along outlet side wall 16, andterminate at the vertical central rib 100 at staggered verticalpositions as compared to the inlet-side ribs 100 such that each ofdrive-side ribs 100 intersect the central vertical rib 100 at adifferent vertical position than each of the inlet-side ribs 100, asshown in FIG. 3. For purposes of the present discussion, the “front” ofpump 10 is considered as the side from which drive shaft 46 projects,and the “back” of pump 10 is the side including inlet aperture 18 andadapter 90. The “front-to-back” direction is substantially perpendicularto the “vertical” direction as illustrated in FIG. 3.

On the vertical face of outlet side wall 16, ribs 100 all emanateradially outwardly from a common center, as best seen in FIG. 8. Inparticular, nine ribs 100 extend radially outwardly along the verticalface from outer drive aperture 22 (FIG. 9), round the corner at thejunction between the vertical and side faces of outlet side wall 16, andextend back to vertical rib 100 as noted above. A similar radiallyoutwardly extending set of six ribs 100 are formed on the vertical faceof inlet side wall 14, as best seen in FIG. 12B.

An alternative casing 12A having a different arrangement of ribs 100A isshown in FIGS. 3A and 3B. For purposes of the present disclosure,casings 12, 12A having ribs 100, 100A respectively are interchangeablewith the other components of pump 10. Accordingly, a reference to casing12 herein is also a reference to casing 12A, unless otherwisespecifically stated. Moreover, casing 12A is substantially similar tocasing 12 described herein, with reference numerals of casing 12Acorresponding to the reference numerals of casing 12, except with an “A”appended thereto. Structures of casing 12 correspond to similarstructures denoted by corresponding reference numerals of casing 12A,except as otherwise noted.

As best seen in FIG. 3A, five ribs 100A extend generally radiallyoutwardly from a central area of outlet side wall 16, similar to theradially arranged ribs 100 described above. However, only the twolowermost ribs 100 extend horizontally from the rim around outer driveaperture 22, round the corner at the junction between the vertical andside faces of outlet side wall 16, and extend backwardly toward inletside wall 14. An uppermost rib 100A extends vertically along thevertical face of outlet side wall 16 but, unlike the lowermost ribs100A, does not join the rim around outer drive aperture 22. Twointermediate ribs 100A are disposed between the lowermost and uppermostribs 100A, and extend radially outwardly from the central area of outletside wall 16. Like the uppermost rib 100A, the intermediate ribs 100A donot join the rim around outer drive aperture 22.

As shown in FIGS. 3A and 3B and in contrast to casing 12 describedabove, casing 12A lacks a vertical rib and does not have any stiffeningribs on inlet side wall 14. In the illustrated embodiment, ribs 100A areprovided only on the high-pressure (i.e., outlet) side of casing 12A, towhich provides resistance to bulging or flexing of outlet side wall 16.However, the size, number and extent of ribs 100A are optimized, asshown in FIG. 3A and described above, to provide this resistance with aminimum of added material and expense. The low-pressure (i.e., inlet)side of casing 12A has no ribs because, in the illustrated application,inlet side wall 14 alone may be sufficient to avoid excessive materialflex from the relatively lower (and negative) pressures experienced ininlet pump chamber 30 (FIG. 5).

The disposition of ribs 100 and 100A only on the exterior surface ofcasings 12 and 12A allows their strengthening function to be met withoutintroduction of stiffening ribs inside pump chambers 30 and 32. Moreparticularly, the portion of inlet pump chamber 30 extending from inletaperture 18 to impeller 44 is free of stiffening ribs along the interiorsurfaces of inlet side wall 14, as well as along the surface ofpartition wall 24 which cooperates with such interior surfaces to forminlet chamber 30. Similarly, the portion of outlet pump chamber 32disposed generally between volute discharge opening 38 and outletaperture 20 is also free of interior ribs along the interior surfaces ofoutlet side wall 16 and the adjacent portion of partition wall 24 whichcooperates with such interior surfaces to form outlet chamber 32.Accordingly, the portions of pump chambers 30 and 32 directly disposedin the flow path of fluid passing through centrifugal pump 10 are freefrom any stiffening ribs or other features designed for selectivestrengthening of inlet side or outlet side walls 14, 16.

Advantageously, the lack of ribs or other stiffening features in theflow paths within casings 12 and 12A facilitates flow with a minimum ofturbulence and eddying, which reduces wear from fluid and solids insuspension while preserving hydraulic efficiency. Meanwhile, theprovision of external ribs 100, 100A as shown in FIGS. 3 and 3A-3Brespectively (described in detail above) provide the strength andrigidity to casings 12, 12A associated with such strengthening features.

2. Volute Discharge

In FIG. 4, volute discharge axis A_(V) is illustrated from the front,i.e., from a perspective facing a “spin plane” of impeller 44 that isperpendicular to its axis of rotation. In FIG. 5, volute discharge axisA_(V) is illustrated from the side, i.e., from a perspective facing avertical center plane containing the axis of rotation of impeller 44.

FIG. 4 illustrates that the spiral-shaped pathway of volute 34 does notterminate in a discharge opening defining a vertical discharge axis, butrather, continues its spiral-shaped pathway to produce the illustratedaxis A_(V) which directs fluid flow from discharge opening 38 across thecenter plane of casing 12 and back toward outlet aperture 20, whichresides on the opposite side of the center plane. Channel 36 is aspiral-shaped structure as illustrated, and defines a correspondinglyspiral-shaped flow axis centrally located in channel 36 and extendingthrough the entire extent of channel 36. As fluid flows through channel36, it follows this spiral-shaped flow axis until it is discharged atdischarge opening 38.

In the illustrated embodiment, discharge axis A_(V) is tangent to thisspiral-shaped flow axis at discharge opening 38, and is oriented or“aimed” to pass directly through outlet aperture 20. In an exemplaryembodiment, axis A_(V) is also perpendicular to a plane defined bydischarge opening 38. This angled and aimed arrangement for axis A_(V)directs pressurized fluid flowing from discharge opening 38 directlytoward outlet aperture 20, thereby minimizing turbulence, decelerationor eddying of fluid along the side walls of outlet side wall 16 ofcasing 12 as the fluid flows toward and through outlet aperture 20.

Turning to the side view of FIG. 5, axis A_(V) is also shown to beforwardly angled with respect to a vertical direction, i.e., angled withrespect to the substantially vertical walls of inlet and outlet sidewalls 14 and 16, while also being non-perpendicular with thesubstantially horizontal base 106 and opposing top portions of inlet andoutlet side walls 14, 16. Moreover, axis A_(V) is generally aimed towardoutlet aperture 20, as viewed in the side section view of FIG. 5, topromote discharge from discharge opening 38 with a maximum volume offluid received at outlet aperture 20 and a minimum volume of fluidtraveling at high speed along partition wall 24 disposed adjacent volute34. Directing flow from discharge opening 38 along a path angled awayfrom the adjacent partition wall 24 avoids frictional interactionbetween the fluid and partition wall 24, and thereby promotes efficientoperation of centrifugal pump 10.

3. Drain Channels

Turning now to FIGS. 11, 12A and 12B, drain channels 132 (FIG. 11) and136 (FIG. 12A) passing through selected locations within casing 12 areillustrated. Drain channels 132, 136 are both in direct fluidcommunication with respective lower portions of outlet pump chamber 32,such that drain plugs 130, 134 (FIG. 12B) respectively can be removed toallow fluid trapped in outlet pump chamber 32 to be drained from casing12 by gravity and without inverting centrifugal pump 10. In particular,both drain channels 132, 136 are in direct fluid communication with asump region 138 formed in a lower portion of casing 12.

In the illustrated embodiment, centrifugal pump 10 is a self-priming“wet prime” pump design. In the illustrated self-priming pump design,casing 12 is designed to retain water or other liquid within sump region138 when pump 10 is not operating. Impeller 44 can draw fluid stored insump region 138 upon activation of pump 10, and can expel any entrappedair from the outlet aperture 20 while picking up additional liquid untila vacuum at inlet aperture 18 is created to draw additional liquid intocasing 12 from the source. At this point, the pump is “primed” and readyfor regular service. As described in detail below, the liquid in sumpregion 138 may be initially introduced into casing 12 via a combinationfill port and flapper access port 82 (FIG. 3). In the context of thepresent disclosure, the “air” in the casing is the non-pumpable fluid(i.e. gas) which resides in the casing during normal operation.

As best seen in FIG. 12A, sump region 138 has a central portion which isin direct fluid communication with impeller 44, while the remainder ofthe sump region is separated from impeller 44 by the wall forming volute34. As illustrated in FIGS. 11 and 12A respectively, drain channels 132,136 are arranged outside the volute flow path and on opposite sides ofvolute 34 and impeller 44, and are therefore in indirect fluidcommunication with the central portion of sump 138 accessed by impeller44. That is, the draining of the central portion of sump 138 via drainchannels 132 and/or 136 would require the fluid to first migrate to theother portions of sump region 138 (i.e., the portions not in directfluid communication with impeller 44), and then enter channel 132 or136.

In this way, drain channels 132, 136 do not form any apertures or otherfeatures which are in direct fluid communication with, or form any partof, volute 34. Therefore, drain channels 132, 136 do not interrupt orotherwise affect the fluid mechanics of impeller 44. For purposes of thepresent disclosure, two distinct fluid areas are in “direct” fluidcommunication if fluid exchange between the two areas does not requirethe fluid flow path to change direction or otherwise “turn a corner.” Bycontrast, two distinct fluid areas are in “indirect” fluid communicationif fluid exchange between the two areas does require the fluid flow pathto change direction or otherwise “turn a corner.”

4. Combination Fill/Inspection Port

Turning now to FIG. 3, port 82 is shown in an upper end of inlet sidewall 14 of casing 12. Port 82 serves as a combination port,accomplishing two functions: access to flapper valve 80 and relatedstructures for, e.g., installation, replacement or maintenance; and as afill port for adding liquid to casing 12, and particularly for addingliquid to sump region 138, shown in FIGS. 1 and 11 and described above.

Turning to FIG. 1, flapper valve 80 is shown in its installed, seatedposition upon inlet adapter 90. In an exemplary embodiment, flappervalve 80 is formed as a resilient polymer or rubber material which bearsagainst the annular inner surface of inlet adapter 90 (i.e., adjacentnecked portion 91) to prevent flow of fluid from inlet pump chamber 30back through inlet aperture 18 and inlet adapter 90, while resilientlybending or “flapping” away from its seated position about a living hinge81 (FIG. 3) so that liquid can be freely admitted to inlet pump chamber30 via inlet adapter 90 and inlet aperture 18. Living hinge 81 connectsflapper valve 80 to a valve mount portion 83, which is attached toadapter 90 by fasteners 88 and retainers 86A, 86B as illustrated.

When centrifugal pump 10 is in service, inlet conduit 140 and outletconduit 142 may both be rigidly affixed to adapters 90, 98,respectively. In addition, base 106 of casing 12 may be affixed to theunderlying surface, such as by mounting bolts 107 shown in FIG. 3. Forthese and other reasons, disconnection of inlet adapter 90 to accessflapper valve 80 and its associated structures may not be practical ortime efficient. However, because flapper valve 80 may be made from arelatively soft and resilient material such as polymer or rubber,relatively frequent inspection, maintenance or repair may be necessary.Combination port 82 offers access to flapper valve 80 from the topportion of centrifugal pump 10, which is typically the most accessibleportion to a service person when pump 10 is mounted in a servicelocation and configuration.

To allow or prevent access to port 82, combination port cover 84 isprovided. When cover 84 is affixed to casing 12 by fasteners 114, fillport cover portion 94 provides a seal (in cooperation with an O-ringpositioned about the periphery of port 82) around flapper access port82, which fluidly isolates inlet pump chamber 30 from the ambientenvironment and thereby allows vacuum or suction pressure to developtherewithin for proper operation of pump 10. When removed, as shown inFIG. 3, port 82 allows a service person to remove fasteners 88,retainers 86A and 86B, and flapper valve 80 for inspection, maintenanceand/or repair. Additionally, because port 82 is offset along afront-to-back direction with respect to flapper valve 80 as shown inFIG. 1, removal of port cover 84 also allows for a visual inspection offlapper valve 80 and its associated structures without removal of thesame from inlet adapter 90.

Turning again to FIG. 3, casing 12 includes fill vent 92 which offersselective fluid communication between outlet pump chamber 32 and theambient environment. Fill vent 92 facilitates the use of combinationport 82 as a fill port for admitting liquid into casing 12, andspecifically to sump region 138 from the inlet side, by allowingdisplaced air to vent to the ambient atmosphere from outlet pump chamber32 via vent 92 as water flows into sump 138 from the inlet side.Combination port cover 84 also serves to fluidly isolate outlet pumpchamber 32 from the ambient environment when cover 84 is installed uponcasing 12, by covering vent 92 with fill vent cover portion 96 (and anO-ring positioned about the periphery of vent 92). As best seen in FIG.3, fill vent cover portion 96 is formed as a forward extension of fillport cover portion 94 in order to pass over partition wall 24 and ontofill vent 92. In the illustrated embodiment, fill port cover portion 94and fill vent cover portion 96 are integrally and monolithically formedas a single component.

In one exemplary embodiment, fasteners 114 used to connect combinationport cover 84 to combination port 82 include an enlarged flat fastenerhead having a fastener aperture 116 formed therethrough. For fieldinspections and maintenance, field surface fasteners 114 facilitateremoval and installation of combination port cover 84 by engagement witha service person's hand, any wrench or clamp capable of engaging theflat head portion of fasteners 114. Alternatively as shown in FIG. 9,rod R may be passed through fastener aperture 116 to gain leverage.

5. Assembly and Alignment of Drive Shaft and Impeller

FIGS. 1, 2 and 10 illustrate the connection between drive shaft 46 andimpeller 44. As described in further detail below, this connectionfacilitates initial assembly and subsequent reassembly by providing acoarse threaded engagement which is easy to thread and difficult tocross-thread. In order to maintain a desired concentricity between therotational axis of impeller 44 and axis A_(D) drive shaft 46, distalnubbin 70 formed on drive shaft 46 defines a tight clearance fit with acorresponding bore 74 formed in impeller 44.

Referring to FIG. 1, drive shaft 46 protrudes from a front surface ofcasing 12 as part of drive mechanism 40 attached thereto. In addition todrive shaft 46, drive mechanism 40 includes a plurality of bearings 47supported by drive shaft housing 42 and rotatably supporting drive shaft46, such that drive shaft 46 can freely rotate with respect to housing42. Drive side wear plate 48 is connected to drive shaft 46 and biasedby a biasing element (illustrated as a compression spring) into firmengagement with drive shaft housing 42 and away from contact withimpeller 44. Cover plate 49 connects to the front (i.e. outer) surfaceof housing 42 to retain and protect bearings 47 (which may be, forexample, a ball bearing or roller bearing). Impeller 44 is fixed todrive shaft 46 (as described further below) and forms the finalcomponent of drive mechanism 40.

When drive mechanism 40 is initially assembled or reassembled (e.g.,after inspection or maintenance) as illustrated in FIG. 10, male threads72 of drive shaft 46 are engaged with the correspondingly formed femalethreads 76 of impeller 44 to affix drive shaft 46 to impeller 44, asbest seen in FIG. 2. In the illustrated embodiment, threads 72 and 76are coarse threads which promote easy initial thread alignment andengagement and correspondingly deter cross-threading or othermis-engagement of male threads 72 with female threads 76. In oneexemplary embodiment, best seen in FIG. 2, threads 72 and 76 aretrapezoidal thread forms, sometimes referred to as “acme” threads, whichprovide a relatively loose thread engagement and a robust resistance tocross-threading. An exemplary embodiment of “coarse” trapezoidal threadsuseable in connection with the present disclosure are Acme “CentralizingScrew Threads” of tolerance class 4C as defined in ANSI/ASME B1.5-1997,the entire disclosure of which is hereby expressly incorporated byreference herein. The use of such coarse trapezoidal threads 72, 76ensure that when drive shaft 46 is inserted through the other componentsof drive mechanism 40 and initially engaged with impeller 44, rotationof drive shaft 46 with respect to impeller 44 in the tighteningdirection causes a reliably proper thread engagement.

Further detail regarding class 4C centralizing threads in accordancewith the present disclosure is provided in Tables 7a, 7b and 8-11 belowand FIG. 13.

TABLE 7a American National Standard Centralizing Acme Single-Start ScrewThreads - Formulas for Determining Diameters (ASME/ANSI B1.5-1988) D =Nominal Size or Diameter in Inches P = Pitch = 1 ÷ Number of Threads perInch No. Classes 2C, 3C, and 4C External Threads (Screws) 1 Major Diam.,Max = D (Basic). 2 Major Diam., Min = D minus tolerance from Table 11,cols. 7, 8, or 10. 3 Pitch Diam., Max = Int. Pitch Diam., Min (Formula9) minus allowance from Table 9, cols. 3, 4, or 5. 4 Pitch Diam., Min =Ext. Pitch Diam., Max (Formula 3) minus tolerance from Table 10. 5 MinorDiam., Max = D minus P minus allowance from Table 11, col. 3. 6 MinorDiam., Min = Ext. Minor Diam., Max (Formula 5) minus 1.5 × Pitch Diam.tolerance from Table 10. Classes 2C, 3C, and 4C Internal Threads (Nuts)7 Major Diam., Min = D plus allowance from Table 11, col. 4. 8 MajorDiam., Max = Int. Major Diam., Min (Formula 7) plus tolerance from Table11, cols. 7, 9, or 11. 9 Pitch Diam., Min = D Minus Pl2 (Basic). 10Pitch Diam., Max = Int. Pitch Diam., Min (Formula 9) plus tolerance fromTable 10. 11 Minor Diam., Min = D minus 0.9P. 12 Minor Diam., Max = Int.Minor Diam., Min (Formula 11) plus tolerance from Table 11, col. 6.

TABLE 7b Limiting Dimensions of American National Standard CentralizingAcme Single- Start Screw Threads, Classes 2C, 3C, and 4C (ASME/ANSIB1.5-1988) Nominal Diameter, D ½ ⅝ ¾ ⅞ 1 1⅛ 1¼ 1⅜ 1½ Threads per Inch*Limiting Diameters 10 8 6 6 5 5 5 4 4 External Threads Classes 2C, 3C,and 4C, Max 0.5000 0.6250 0.7500 0.8750 1.0000 1.1250 1.2500 1.37501.5000 Major Diameter Class 2C, Major Diameter Min 0.4975 0.6222 0.74700.8717 0.9965 1.1213 1.2461 1.3709 1.4957 Class 3C, Major Diameter Min0.4989 0.6238 0.7487 0.8736 0.9985 1.1234 1.2483 1.3732 1.4982 Class 4C,Major Diameter Min 0.4993 0.6242 0.7491 0.8741 0.9990 1.1239 1.24891.3738 1.4988 Classes 2C, 3C, and 4C, Max 0.3800 0.4800 0.5633 0.68830.7800 0.9050 1.0300 1.1050 1.2300 Minor Diameter Class 2C, MinorDiameter Min 0.3594 0.4570 0.5371 0.6615 0.7509 0.8753 0.9998 1.07191.1965 Class 3C, Minor Diameter Min 0.3704 0.4693 0.5511 0.6758 0.76640.8912 1.0159 1.0896 1.2144 Class 4C, Minor Diameter Min 0.3731 0.47230.5546 0.6794 0.7703 0.8951 1.0199 1.0940 1.2188 Max 0.4443 0.55620.6598 0.7842 0.8920 1.0165 1.1411 1.2406 1.3652 Class 2C, PitchDiameter {open oversize brace} Min 0.4306 0.5408 0.6424 0.7663 0.87260.9967 1.1210 1.2186 1.3429 Max 0.4458 0.5578 0.6615 0.7861 0.89401.0186 1.1433 1.2430 1.3677 Class 3C, Pitch Diameter {open oversizebrace} Min 0.4394 0.5506 0.6534 0.7778 0.8849 1.0094 1.1339 1.23271.3573 Max 0.4472 0.5593 0.6632 0.7880 0.8960 1.0208 1.1455 1.24531.3701 Class 4C, Pitch Diameter {open oversize brace} Min 0.4426 0.55420.6574 0.7820 0.8895 1.0142 1.1388 1.2380 1.3627 Internal ThreadsClasses 2C, 3C, and 4C, Min 0.5007 0.6258 0.7509 0.8759 1.0010 1.12611.2511 1.3762 1.5012 Major Diameter Classes 2C and 3C, Major Max 0.50320.6286 0.7539 0.8792 1.0045 1.1298 1.2550 1.3803 1.5055 Diameter Class4C, Major Diameter Max 0.5021 0.6274 0.7526 0.8778 1.0030 0.1282 1.25331.3785 1.5036 Classes 2C, 3C, and 4C, Min 0.4100 0.5125 0.6000 0.72500.8200 0.9450 0.0700 1.1500 1.2750 Minor Diameter Max 0.4150 0.51870.6083 0.7333 0.8300 0.9550 1.0800 1.1625 1.2875 Min 0.4500 0.56250.6667 0.7917 0.9000 1.0250 1.1500 1.2500 1.3750 Class 2C, PitchDiameter {open oversize brace} Max 0.4637 0.5779 0.6841 0.8096 0.91941.0448 1.1701 1.2720 1.3973 Min 0.4500 0.5625 0.6667 0.7917 0.90001.0250 1.1500 1.2500 1.3750 Class 3C, Pitch Diameter {open oversizebrace} Max 0.4564 0.5697 0.6748 0.8000 0.9091 1.0342 1.1594 1.26031.3854 Min 0.4500 0.5625 0.6667 0.7917 0.9000 1.0250 1.1500 1.25001.3750 Class 4C, Pitch Diameter {open oversize brace} Max 0.4546 0.56760.6725 0.7977 0.9065 1.0316 1.1567 1.2573 1.3824 Nominal Diameter, D 1¾2 2¼ 2½ 2¾ 3 3½ 4 4½ 5 Threads per Inch* Limiting Diameters 4 4 3 3 3 22 2 2 2 External Threads Classes 2C, 3C, and 4C, Max 1.7500 2.00002.2500 2.5000 2.7500 3.0000 3.5000 4.0000 4.5000 5.0000 Major DiameterClass 2C, Major Diameter Min 1.7454 1.9951 2.2448 2.4945 2.7442 2.99393.4935 3.9930 4.4926 4.9922 Class 3C, Major Diameter Min 1.7480 1.99792.2478 2.4976 2.7475 2.9974 3.4972 3.9970 4.4968 4.9966 Class 4C, MajorDiameter Min 1.7487 1.9986 2.2485 2.4984 2.7483 2.9983 3.4981 3.99804.4979 4.9978 Classes 2C, 3C, and 4C, Max 1.4800 1.7300 1.8967 2.14672.3967 2.4800 2.9800 3.4800 3.9800 4.4800 Minor Diameter Class 2C, MinorDiameter Min 1.4456 1.6948 1.8572 2.1065 2.3558 2.4326 2.9314 3.43023.9291 4.4281 Class 3C, Minor Diameter Min 1.4640 1.7136 1.8783 2.12792.3776 2.4579 2.9574 3.4568 3.9563 4.4558 Class 4C, Minor Diameter Min1.4685 1.7183 1.8835 2.1333 2.3831 2.4642 2.9638 3.4634 3.9631 4.4627Max 1.6145 1.8637 2.0713 2.3207 2.5700 2.7360 3.2350 3.7340 4.23304.7319 Class 2C, Pitch Diameter {open oversize brace} Min 1.5916 1.84022.0450 2.2939 2.5427 2.7044 3.2026 3.7008 4.1991 4.6973 Max 1.61711.8665 2.0743 2.3238 2.5734 2.7395 3.2388 3.7380 4.2373 4.7364 Class 3C,Pitch Diameter {open oversize brace} Min 1.6064 1.8555 2.0620 2.31132.5607 2.7248 3.2237 3.7225 4.2215 4.7202 Max 1.6198 1.8693 2.07732.3270 2.5767 2.7430 3.2425 3.7420 4.2415 4.7409 Class 4C, PitchDiameter {open oversize brace} Min 1.6122 1.8615 2.0685 2.3181 2.56762.7325 3.2317 3.7309 4.2302 4.7294 Internal Threads Classes 2C, 3C, and4C, Min 1.7513 2.0014 2.2515 2.5016 2.7517 3.0017 3.5019 4.0020 4.50215.0022 Major Diameter Classes 2C and 3C, Major Max 1.7559 2.0063 2.25672.5071 2.7575 3.0078 3.5084 4.0090 4.5095 5.0100 Diameter Class 4C,Major Diameter Max 1.7539 2.0042 2.2545 2.5048 2.7550 3.0052 3.50564.0060 4.5063 5.0067 Classes 2C, 3C, and 4C, Min 1.5250 1.7750 1.95002.2000 2.4500 2.5500 3.0500 3.5500 4.0500 4.5500 Minor Diameter Max1.5375 1.7875 1.9667 2.2167 2.4667 2.5750 3.0750 3.5750 4.0750 4.5750Min 1.6250 1.8750 2.0833 2.3333 2.5833 2.7500 3.2500 3.7500 4.25004.7500 Class 2C, Pitch Diameter {open oversize brace} Max 1.6479 1.89852.1096 2.3601 2.6106 2.7816 3.2824 3.7832 4.2839 4.7846 Min 1.62501.8750 2.0833 2.3333 2.5833 2.7500 3.2500 3.7500 4.2500 4.7500 Class 3C,Pitch Diameter {open oversize brace} Max 1.6357 1.8860 2.0956 2.34582.5960 2.7647 3.2651 3.7655 4.2658 4.7662 Min 1.6250 1.8750 2.08332.3333 2.5833 2.7500 3.2500 3.7500 4.2500 4.7500 Class 4C Pitch Diameter{open oversize brace} Max 1.6326 1.8828 2.0921 2.3422 2.5924 2.76053.2608 3.7611 4.2613 4.7615 *All other dimensions are in inches. Theselection of threads per inch is arbitrary and for the purpose ofestablishing a standard.

TABLE 8 American National Standard Centralizing Acme Single-Start ScrewThread Data (ASME/ANSI B1.5-1988) Diameters Thread Data Centralizing,Classes Lead Angle at Basic Identification 2C, 3C, and 4C PitchDiameter* Threads Basic Pitch Minor Basic Basic Centralizing Nominal perMajor Diameter, Diameter, Thickness at Height of Width Classes 2C, SizesInch,* Diameter, D₂ = D₁ = Pitch, Pitch Line, Thread, of Flat, 3C, and4C, λ (All Classes) n D (D − h) (D − 2h) P t = P/2 h = P/2 F = 0.3707PDeg Min ¼ 16 0.2500 0.2188 0.1875 0.06250 0.03125 0.03125 0.0232 5 125/16 14 0.3125 0.2768 0.2411 0.07143 0.03571 0.03571 0.0265 4 42 ⅜ 120.3750 0.3333 0.2917 0.08333 0.04167 0.04167 0.0309 4 33 7/16 12 0.43750.3958 0.3542 0.08333 0.04167 0.04167 0.0309 3 50 ½ 10 0.5000 0.45000.4000 0.10000 0.05000 0.05000 0.0371 4 3 ⅝ 8 0.6250 0.5625 0.50000.12500 0.06250 0.06250 0.0463 4 3 ¾ 6 0.7500 0.6667 0.5833 0.166670.08333 0.08333 0.0618 4 33 ⅞ 6 0.8750 0.7917 0.7083 0.16667 0.083330.08333 0.0618 3 50 1 5 1.0000 0.9000 0.8000 0.20000 0.10000 0.100000.0741 4 3 1⅛ 5 1.1250 1.0250 0.9250 0.20000 0.10000 0.10000 0.0741 3 331¼ 5 1.2500 1.1500 1.0500 0.20000 0.10000 0.10000 0.0741 3 10 1⅜ 41.3750 1.2500 1.1250 0.25000 0.12500 0.12500 0.0927 3 39 1½ 4 1.50001.3750 1.2500 0.25000 0.12500 0.12500 0.0927 3 19 1¾ 4 1.7500 1.62501.5000 0.25000 0.12500 0.12500 0.0927 2 48 2 4 2.0000 1.8750 1.75000.25000 0.12500 0.12500 0.0927 2 26 2¼ 3 2.2500 2.0833 1.9167 0.333330.16667 0.16667 0.1236 2 55 2½ 3 2.5000 2.3333 2.1667 0.33333 0.166670.16667 0.1236 2 36 2¾ 3 2.7500 2.5833 2.4167 0.33333 0.16667 0.166670.1236 2 21 3 2 3.0000 2.7500 2.5000 0.50000 0.25000 0.25000 0.1853 3 193½ 2 3.5000 3.2500 3.0000 0.50000 0.25000 0.25000 0.1853 2 48 4 2 4.00003.7500 3.5000 0.50000 0.25000 0.25000 0.1853 2 26 4½ 2 4.5000 4.25004.0000 0.50000 0.25000 0.25000 0.1853 2 9 5 2 5.0000 4.7500 4.50000.50000 0.25000 0.25000 0.1853 1 55 *All other dimensions are given ininches.

TABLE 9 American National Standard Centralizing Acme Single-Start ScrewThreads - Pitch Diameter Allowances (ASME/ANSI B1.5-1988) Allowances onExternal Threads† Centralizing Nominal Size Range* Class 2C, Class 3C,Class 4C, Above To and Including 0.008{square root over (D)}0.006{square root over (D)} 0.004{square root over (D)} 0 3/16 0.00240.0018 0.0012 3/16 5/16 0.0040 0.0030 0.0020 5/16 7/16 0.0049 0.00370.0024 7/16 9/16 0.0057 0.0042 0.0028 9/16 11/16 0.0063 0.0047 0.003211/16 13/16 0.0069 0.0052 0.0035 13/16 15/16 0.0075 0.0056 0.0037 15/161 1/16 0.0080 0.0060 0.0040 1 1/16 1 3/16 0.0085 0.0064 0.0042 1 3/16 15/16 0.0089 0.0067 0.0045 1 5/16 1 7/16 0.0094 0.0070 0.0047 1 7/16 19/16 0.0098 0.0073 0.0049 1 9/16 1⅞ 0.0105 0.0079 0.0052 1⅞ 2⅛ 0.01130.0085 0.0057 2⅛ 2⅜ 0.0120 0.0090 0.0060 2⅜ 2⅝ 0.0126 0.0095 0.0063 2⅝2⅞ 0.0133 0.0099 0.0066 2⅞ 3¼ 0.0140 0.0105 0.0070 3¼ 3¾ 0.0150 0.01120.0075 3¾ 4¼ 0.0160 0.0120 0.0080 4¼ 4¾ 0.0170 0.0127 0.0085 4¾ 5½0.0181 0.0136 0.0091 All dimensions are given in inches. *The values incols. 3 to 5 are to be used for any size within the range shown in cols.1 and 2. These values are calculated from the mean of the range. It isrecommended that the sizes given in Table 8 be ued whenever possible.†An increase of 10 percent in the allowance is recommended for eachinch, or fraction thereof, that the length of engagement exceeds twodiameters.

TABLE 10 American National Standard Centralizing Acme Single-Start ScrewThreads - Pitch Diameter Tolerances¹ (ASME/ANSI B1.5-1988) (For anyparticular size of thread, the pitch diameter tolerance is obtained byadding the diameter increment from the upper half of the table to thepitch increment from the lower half of the table. Example: A 0.250-16-ACME-2C thread has a pitch diameter tolerance of 0.00300 + 0.00750 =0.0105 inch.) Class of Thread 2C 3C 4C Nom. Dimeter Increment Dia.,² D.006{square root over (D)} .0028{square root over (D)} .002{square rootover (D)} ¼ .00300 .00140 .00100 5/16 .00335 .00157 .00112 ⅜ .00367.00171 .00122 7/16 .00397 .00185 .00132 ½ .00424 .00198 .00141 ⅝ .00474.00221 .00158 ¾ .00520 .00242 .00173 ⅞ .00561 .00262 .00187 1 .00600.00280 .00200 1⅛ .00636 .00297 .00212 1¼ .00671 .00313 .00224 1⅜ .00704.00328 .00235 1½ .00735 .00343 .00245 1¾ .00794 .00370 .00265 2 .00849.00396 .00283 2¼ .00900 .00420 .00300 2½ .00949 .00443 .00316 2¾ .00995.00464 .00332 3 .01039 .00485 .00346 3½ .01122 .00524 .00374 4 .01200.00560 .00400 4½ .01273 .00594 .00424 5 .01342 .00626 .00447 . . . . . .. . . . . . Class of Thread 2C 3C 4C Thds. per Pitch Increment Inch, n.030{square root over (1/n)} .014{square root over (1/n)} .010{squareroot over (1/n)} 16 .00750 .00350 .00250 14 .00802 .00374 .00267 12.00866 .00404 .00289 10 .00949 .00443 .00316 8 .01061 .00495 .00354 6.01225 .00572 .00408 5 .01342 .00626 .00447 4 .01500 .00700 .00500 3.01732 .00808 .00577 2½ .01897 .00885 .00632 2 .02121 .00990 .00707 1½.02449 .01143 .00816 1⅓ .02598 .01212 .00866 1 .03000 .01400 .01000 Alldimensions are given in inches. ¹The equivalent tolerance on threadthickness is 0.259 times the pitch diameter tolerance. ²For a nominaldiameter between any two tabulated nominal diameters, use the diameterincrement for the larger of the two tabulated nominal diameters.

TABLE 11 American National Standard Centralizing Acme Single-Start ScrewThreads - Tolerances and Allowances for Major and Minor Diameters**(ASME/ANSI B1.5-1988) Allowance From Basic Major and Toler. Tolerance onMajor Diameter Plus Minor-Diameters (All Classes) on Minor on Internal,Minus on External Threads Minor Diam.*** Class 2C Diam.† Internal ThreadAll External All Major Minor Internal and Class 3C Class 4C Thds*External Diam.‡ Diam.† Threads, Internal External Internal ExternalInternal Size per Threads (Plus (Plus (Plus Threads, Thread, Thread,Thread, Thread, (Nom.) Inch (Minus) 0.0010{square root over (D)}) 0.1P)0.05P) 0.0035{square root over (D)} 0.0015{square root over (D)}0.0035{square root over (D)} 0.0010{square root over (D)} 0.0020{squareroot over (D)} ¼ 16 0.010 0.0005 0.0062 0.0050 0.0017 0.0007 0.00170.0005 0.0010 5/16 14 0.010 0.0006 0.0071 0.0050 0.0020 0.0008 0.00200.0006 0.0011 ⅜ 12 0.010 0.0006 0.0083 0.0050 0.0021 0.0009 0.00210.0006 0.0012 7/16 12 0.010 0.0007 0.0083 0.0050 0.0023 0.0010 0.00230.0007 0.0013 ½ 10 0.020 0.0007 0.0100 0.0050 0.0025 0.0011 0.00250.0007 0.0014 ⅝ 8 0.020 0.0008 0.0125 0.0062 0.0028 0.0012 0.0028 0.00080.0016 ¾ 6 0.020 0.0009 0.0167 0.0083 0.0030 0.0013 0.0030 0.0009 0.0017⅞ 6 0.020 0.0009 0.0167 0.0083 0.0033 0.0014 0.0033 0.0009 0.0019 1 50.020 0.0010 0.0200 0.0100 0.0035 0.0015 0.0035 0.0010 0.0020 1⅛ 5 0.0200.0011 0.0200 0.0100 0.0037 0.0016 0.0037 0.0011 0.0021 1¼ 5 0.0200.0011 0.0200 0.0100 0.0039 0.0017 0.0039 0.0011 0.0022 1⅜ 4 0.0200.0012 0.0250 0.0125 0.0041 0.0018 0.0041 0.0012 0.0023 1½ 4 0.0200.0012 0.0250 0.0125 0.0043 0.0018 0.0043 0.0012 0.0024 1¾ 4 0.0200.0013 0.0250 0.0125 0.0046 0.0020 0.0046 0.0013 0.0026 2 4 0.020 0.00140.0250 0.0125 0.0049 0.0021 0.0049 0.0014 0.0028 2¼ 3 0.020 0.00150.0333 0.0167 0.0052 0.0022 0.0052 0.0015 0.0030 2½ 3 0.020 0.00160.0333 0.0167 0.0055 0.0024 0.0055 0.0016 0.0032 2¾ 3 0.020 0.00170.0333 0.0167 0.0058 0.0025 0.0058 0.0017 0.0033 3 2 0.020 0.0017 0.05000.0250 0.0061 0.0026 0.0061 0.0017 0.0035 3½ 2 0.020 0.0019 0.05000.0250 0.0065 0.0028 0.0065 0.0019 0.0037 4 2 0.020 0.0020 0.0500 0.02500.0070 0.0030 0.0070 0.0020 0.0040 4½ 2 0.020 0.0021 0.0500 0.02500.0074 0.0032 0.0074 0.0021 0.0042 5 2 0.020 0.0022 0.0500 0.0250 0.00780.0034 0.0078 0.0022 0.0045 *All other dimensions are given in inches.Intermediate pitches take the values of the next coarser pitch listed.**Values for intermediate diameters should be calculated from theformulas in column headings, but ordinarily may be interpolated. ***Toavoid a complicated formula and still provide an adequate tolerance, thepitch factor is used as a basis, with the minimum tolerance set at 0.005in. †The minimum clearance at the minor diameter between the internaland external thread is the sum of the values in columns 3 and 5. ‡Theminimum clearance at the major diameter between the internal andexternal thread is equal to col. 4. Tolerance on minor diameter of allexternal threads is 1.5 × pitch diameter tolerance.

When threads 72, 76 are fully engaged, impeller 44 becomes rotatablyfixed in the drive direction to the distal end of drive shaft 46. Thatis to say, when impeller is rotated in the fluid-accelerating directionby drive shaft 46, the engagement of threads 72, 76 tends to betightened and the full engagement of threads 72, 76 is maintained. Whenimpeller 44 is rotated in the opposite (i.e., non-functional) direction,threads 72, 76 will tend to disengage. Thus, to connect drive shaft 46to impeller 44, impeller 44 is immobilized and drive shaft 46 is rotatedin the tightening direction until threads 72, 76 are engaged. Subsequentoperation of pump 10 will ensure that this engagement is maintained, andtherefore drive shaft 46 is selectively rotatably fixed to impeller 44.To disconnect drive shaft 46 from impeller 44, impeller 44 isimmobilized and drive shaft 46 is rotated in the opposite direction todisengage threads 72, 76.

As male threads 72 and female threads 76 approach full engagement asshown in FIG. 2, distal nubbin 70 formed at the end of drive shaft 46encounters a correspondingly formed bore 74 formed in impeller 44. Bothnubbin 70 and bore 74 may be machined to a tight tolerance in order toconcentrically align drive shaft 46 and impeller 44 with a precise andclose-tolerance fit upon final assembly. In one exemplary embodiment,the total radial clearance between distal nubbin 70 and bore 74 is lessthan 0.004 inches, such as between 0.001 inches and 0.003 inches.Advantageously, the interaction between nubbin 70 and bore 74 reduces oreliminates any non-concentricity between drive shaft axis A_(D) and theintended rotational axis of impeller 44. In an exemplary embodiment, thethreaded connection formed by threads 72, 76 allows for a relativelylarge radial play of drive shaft axis A_(D) relative to the rotationalaxis of impeller 44. That is, when drive shaft 46 is connected to bythreads 72, 76 and not by nubbin 70 and bore 74, the opposite end ofdrive shaft 46 is allowed to move radially such that drive shaft axisA_(D) becomes angled with respect to the rotational axis of impeller 44.

In one exemplary embodiment, this radial play may be between 0.001inches and 0.003 inches, as defined in ANSI/ASME B1.5-1997, the entiredisclosure of which is hereby expressly incorporated by referenceherein. By contrast, when nubbin 70 and bore 74 are engaged in additionto threads 72, 76 such that impeller 44 is tightened fully against theadjacent shoulder of drive shaft 46, this radial play is eliminated anddrive shaft axis A_(D) becomes substantially concentric with therotational axis of impeller 44.

Although drive shaft 46 includes the male features used to connect driveshaft 46 to impeller 44 (i.e., male threads 72 and nubbin 70) andimpeller 44 includes the female features (i.e., female threads 76 andbore 74), it is contemplated that this arrangement can be reversed asrequired or desired for a particular design. That is, either componentcan be provided with male threads 72 and the other component can beprovided with the corresponding female threads 76. Similarly, eithercomponent can be provided with a male centering feature such as nubbin70, and the other component can be provided with the correspondingfemale feature such as bore 74.

6. Drive Disassembly System

Turning now to FIGS. 8 and 9, drive disassembly system 50 used fordisconnecting and connecting drive mechanism 40 from casing 12 and theremainder of pump 10 is illustrated. As described below, the componentsof drive disassembly system 50 may be connected to pump 10 when tofacilitate removal and/or installation of drive mechanism 40, and can bedisconnected from pump 10 during regular operation.

Drive disassembly system 50 includes guide rail 52 selectively receivedwithin blind bore 66 (FIG. 1) formed in a central stiffener 28.Stiffener 28 extends along a front-to-back direction from the verticalportion of outlet side wall 16 to partition wall 24, and provides astructural support which inhibits bulging or deflection of outlet sidewall 16 under the high pressures developed within outlet pump chamber32. The strength and structural integrity afforded by stiffener 28 andits associated structures also firmly supports guide rail 52 within bore66.

In an exemplary embodiment, guide rail 52 is snugly received in bore 66.For example, the total radial clearance between guide rail 52 and bore66 may be between 0.0015 inches and 0.0055 inches. When so snuglyreceived, guide rail 52 has minimal radial play and therefore firmlysupports drive mechanism 40 during assembly and disassembly proceduresas described further below.

In order to axially fix guide rail 52 in its fully received position inbore 66, rail keeper 56 may be used to engage notch 54 formed in guiderail 52 (FIG. 9). Rail keeper 56 may then be fastened to casing 12 inorder to axially fix rail keeper 56 and guide rail 52 to casing 12.

Rail guide 58 includes bearing 60 sized to be slidingly received overguide rail 52, and flange 62 is fixed to bearing 60 (e.g., by welding).

When drive disassembly system 50 is used to remove drive mechanism 40from casing 12, guide rail is first installed as described above. Aportion of the standard installation fasteners 43 holding drivemechanism 40 in place (FIG. 1) are removed, such as the four fasteners43 closest to guide rail 52. Bearing 60 is then slid onto the previouslyinstalled guide rail 52 until flange 62 of rail guide 58 abuts casing12, as shown in FIG. 8. Fasteners 65 are passed through apertures 64(not shown) formed in of flange 62 to bolt rail guide 58 to drivemechanism 40 at the locations where standard fasteners 43 were removed.In an exemplary embodiment, apertures 64 through flange 62 are oversizedrelative to fasteners 65, which allows fasteners 65 to move slightlywithin apertures 64 such that alignment of drive disassembly system 50relative to casing 12 can be controlled by interaction between guiderail 52 and bearing 60, rather than between flange 62 and casing 12.

Fasteners 65 used in connection with drive disassembly system 50 arelarger than standard fasteners 43 used to secure drive shaft housing 42to casing 12 (FIG. 1). In this way, fasteners 43 are allowed passthrough the threaded apertures 64 in the flange of drive shaft housing42 (i.e., without threadably engaging threaded apertures 64), butfasteners 65 threadably connect to apertures 64. In this way, drivemechanism 40 is fixed to casing 12 by fasteners 43, while rail guide 58is fixed to housing 42 by the larger threaded fasteners 65.

With rail guide 58 affixed to drive shaft housing 42 and slidinglyreceived upon guide rail 52, drive mechanism 40 is ready to be removedfrom outer drive aperture 22 formed in outlet side wall 16 of casing 12,as illustrated in FIG. 9. Any remaining fasteners 43 affixing driveshaft housing 42 to casing 12 are removed to free drive mechanism 40from the remainder of pump 10.

Turning to FIG. 9, drive mechanism 40 may then be pulled free of casing12 using guide rail 52 for support of drive mechanism 40.Advantageously, guide rail 52 accepts the weight of drive mechanism 40,allowing the service person to focus on guiding drive mechanism 40safely free of casing 12 without having to also support the weightmanually. In addition, caster 68 may be affixed to a lower portion ofdrive shaft housing 42, such as by caster bracket 69, in order tocooperate with guide rail 52 to provide support for the weight of drivemechanism 40 during removal or installation in casing 12. In theillustrated embodiment, standard fasteners 43 may be removed along thebottom portion of housing 42 to expose threaded apertures 64 (notshown), such that fasteners 65 can be threadably engaged with apertures64 to affix bracket 69 to housing 42 in a similar fashion to rail guide58 described above.

For installation or reinstallation of drive mechanism 40 via drivedisassembly system 50, the steps of removal are simply repeated inreverse. During final alignment of drive mechanism 40, after it isreceived in outer drive aperture 22 and through inner drive aperture 26(FIG. 5), fasteners 65 may be loosened as needed to allow for any neededreadjustment.

7. Impeller Inspection

Turning now to FIG. 11, inspection cover 110 and inspection side wearplate 112 are shown removed from their seated positions within casing 12to expose outer inspection aperture 124 leading to inlet pump chamber30, as well as inner inspection aperture 126 leading to volute 34, fluidchannel 36 and impeller 44 seated in the central bore of volute 34.

In an exemplary embodiment, inspection side wear plate 112 is fixed toinspection cover 110, such as by fasteners. When so fixed, removal ofinspection cover 110 also removes inspection side wear plate 112 as asingle unit to allow access to inlet pump chamber 30, volute 34 andimpeller 44 for inspection, maintenance or repair. When inspection cover110 and wear plate 112 are reinstalled to casing 12 through outerinspection aperture 124, the previous spacing and configuration betweenthe wear surface of wear plate 112 and the adjacent bearing surface ofimpeller 44 is maintained.

In order to set and maintain such proper spacing, fastener 114 may beused to affix inspection cover 110 and inspection side wear plate 112 tocasing 12 via cannulated bolt 118 and bolt fixation plate 120. Only oneof this fastener arrangement is illustrated in FIG. 11 for clarity, itbeing understood that the illustrative embodiment uses four suchfastener arrangements for each of fastener apertures 116 formed ininspection cover 110.

Fastener apertures 116 are threaded to receive the correspondinglythreaded shaft of cannulated bolt 118. The length of the threadedportion of cannulated bolt 118 is such that each bolt 118 may protrudebeyond the distal end of aperture 116 to bear against the adjacent faceof casing 12, which prevents inspection cover 110 from fully seatingagainst casing 12 because the distal end of bolts 118 contact casing 12before cover 110. In this way, the spacing of inspection side wear plate112 from impeller 44 can be controlled by adjusting cannulated bolts 118to protrude more or less beyond the distal end of fastener apertures116.

In order to rotationally fix cannulated bolts 118 in a desired positioncorresponding to proper axial spacing between wear plate 112 andimpeller 44, fixation plate 120 and fastener 122 are provided. Fixationplate 120 includes a bolt head receiving aperture 121 which is generallypolygonal in order to rotationally fix cannulated bolt 118 to fixationplate 120 when the hexagonal head of bolt 118 is received withinaperture 121. In an exemplary embodiment, aperture 121 is a “twelvepoint” style of the type commonly used in wrenches and sockets anddesigned to rotatably fix to hex bolt heads. Aperture 121 is placed overthe head of bolt 118, such that fastener slot 123 aligns with fixationaperture 117 formed in inspection cover 110. Fastener 122 is then passedthrough slot 123 and into threaded engagement with aperture 117,rotationally and axially fixing bolt fixation plate 120 to inspectioncover 110, and therefore fixing the rotational orientation and axialadjustment of cannulated bolt 118. Fastener 114 (described in detailabove) is then passed through the central bore of cannulated bolt 118and threadably engaged with the adjacent threaded aperture of casing 12to affix inspection cover 110 thereto.

While this invention has been described as having an exemplary design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

What is claimed is:
 1. A centrifugal pump comprising: a drive mechanism;an impeller drivingly connected to the drive mechanism; a casing havingan inlet and an outlet, the casing comprising: an inlet-side wall havingan inlet aperture formed therein; an outlet-side wall joined to theinlet-side wall to form a cavity within the casing, the outlet-side wallhaving an outlet aperture; a volute disposed in the casing and in fluidcommunication with the inlet aperture and the outlet aperture, thevolute having a central opening sized to receive the impeller and aspiral-shaped fluid channel such that the fluid channel progressesradially outwardly toward a volute discharge opening, the volutedischarge opening defining a longitudinal discharge axis which extendsthrough the outlet aperture, whereby the volute is adapted to receivefluid accelerated outwardly by the impeller, direct the fluid radiallyoutwardly through the spiral-shaped fluid channel, and discharge thefluid along the longitudinal discharge axis toward the outlet aperture.2. The centrifugal pump of claim 1, wherein the casing defines avertical center plane containing an axis of rotation of the impeller,and the longitudinal discharge axis is oriented to cross the verticalcenter plane.
 3. The centrifugal pump of claim 1, wherein the impellerdefines a spin plane perpendicular to the axis of impeller rotation, thedischarge axis is angled with respect to the spin plane.
 4. Thecentrifugal pump of claim 3, wherein the casing further comprises apartition wall interposed between the inlet-side wall and theoutlet-side wall to form an inlet pump chamber and an outlet pumpchamber, the partition wall having an inner drive aperture positioned toallow fluid communication between the inlet pump chamber and the outletpump chamber via the inner drive aperture.
 5. The centrifugal pump ofclaim 4, wherein the discharge axis is angled away from the partitionwall.
 6. The centrifugal pump of claim 4, wherein the casing furthercomprises a plurality of fastener bosses disposed within the outlet pumpchamber and adjacent the outlet aperture, the fastener bosses eachhaving a smooth, rounded outer surface.
 7. The centrifugal pump of claim6, wherein the fastener bosses each have a convex distal surface and aconcave surface at the junction between the convex distal surface andthe adjacent inner surface of the outlet pump chamber.
 8. Thecentrifugal pump of claim 6, wherein the fastener bosses define a teardrop shape with a pointed end of the tear drop shape pointing toward theoutlet aperture, whereby the fastener bosses promote laminar flow offluid discharged from the volute and advanced toward the outletaperture.
 9. The centrifugal pump of claim 4, wherein the casing of thepump comprises a sump region formed in a lower region of the outlet pumpchamber, the sump region including a central portion in direct fluidcommunication with the impeller and a peripheral portion in indirectfluid communication with the impeller, the casing further comprising atleast one drain channel in direct fluid communication with theperipheral portion of the sump region and in indirect fluidcommunication with the central portion of the sump region, whereby theat least one drain channel does not form any part of the volute.
 10. Thecentrifugal pump of claim 9, wherein the casing comprises a first drainchannel and a second drain channel, the first and second drain channelspositioned on opposite side of the volute.
 11. The centrifugal pump ofclaim 1, wherein the pump further comprises an inlet adapter connectedto the inlet aperture, the inlet adapter including a necked portion inwhich a flow area through the inlet adapter gradually increases along aflow direction toward the inlet aperture.
 12. The centrifugal pump ofclaim 11, wherein: the pump further comprises an outlet adapterconnected to the outlet aperture, the outlet adapter having asubstantially cylindrical fluid passage, and the inlet and outletadapters configured to receive a common nominal size of fluid conduitand the necked portion of the inlet adapter leading to the inletaperture having larger area than the outlet aperture.
 13. Thecentrifugal pump of claim 1, wherein the outlet aperture comprises anoutlet transition area having a radiused internal edge operable tofacilitate smooth flow therethrough, the outlet transition area defininga nominal radius at least equal to a minimum thickness of theoutlet-side wall.
 14. The centrifugal pump of claim 13, wherein thenominal radius of the outlet transition area is at least 131% of theminimum thickness of the outlet-side wall.
 15. The centrifugal pump ofclaim 1, further comprising a plurality of stiffening ribs extendingalong and integrally formed with the inlet-side wall and the outlet-sidewall of the casing, the stiffening ribs disposed only on an exteriorsurface of the casing.
 16. The centrifugal pump of claim 15, wherein aplurality of ribs on the outlet-side wall extend along a substantiallyvertical face of the outlet-side wall, round a corner at the junctionbetween the vertical face a side face of the outlet-side wall, andextend along a front-to-back direction on the side face.
 17. Thecentrifugal pump of claim 16, wherein the plurality of extend radiallyoutwardly along the vertical face from a central area of the verticalface.
 18. The centrifugal pump of claim 1, wherein the outlet-side wallof the casing comprises an outer drive aperture sized to receive thedrive mechanism.
 19. A centrifugal pump comprising: a drive mechanism;an impeller drivingly connected to the drive mechanism; a flapper valve;a casing having an inlet and an outlet, the casing comprising: aninlet-side wall having an inlet aperture formed therein, the flappervalve positioned at the inlet aperture to admit a flow of fluid into thecasing via the inlet aperture while preventing a flow of fluid out ofthe casing via the inlet aperture; an outlet-side wall joined to theinlet-side wall to form a cavity within the casing, the outlet-side wallhaving an outlet aperture; a partition wall interposed between theinlet-side wall and the outlet-side wall to form an inlet pump chamberand an outlet pump chamber, the partition wall having an inner driveaperture positioned to allow fluid communication between the inlet pumpchamber and the outlet pump chamber via the inner drive aperture; acombination port formed in the casing near the flapper valve, thecombination port sized and positioned to allow access to the flappervalve by a maintenance person, and to allow fluid to be added to theinlet pump chamber; and a fill vent formed through the casing on anopposite side of the partition wall as the combination port, such thatthe fill vent allows fluid communication between the outlet pump chamberand the ambient environment, whereby liquid added to the inlet pumpchamber is allowed to flow to the outlet pump chamber via the innerdrive aperture while air contained in the outlet pump chamber vents toatmosphere via the fill vent.
 20. The centrifugal pump of claim 19,further comprising a combination port cover comprising: a fill portcover portion sized to be received over the combination port to fluidlyisolate the combination port from the ambient environment; and a fillvent cover portion sized to be received over the fill vent to fluidlyisolate the fill vent from the ambient environment.
 21. The centrifugalpump of claim 20, wherein the fill vent cover portion is formed as aforward extension of the fill port cover portion in order to pass overthe partition wall onto the fill vent.
 22. The centrifugal pump of claim20, wherein the fill port cover portion and the fill vent cover portionare integrally, monolithically formed as a single component.
 23. Thecentrifugal pump of claim 19, wherein the outlet-side wall of the casingcomprises an outer drive aperture formed therein, the outer driveaperture sized to receive the drive mechanism.
 24. A centrifugal pumpcomprising: a drive shaft having a first coarse thread and a firstcentering feature; an impeller drivingly connected to the drive shaft,the impeller having a second coarse thread and a second centeringfeature, the second coarse thread engageable with the first coarsethread of the drive shaft to selectively rotatably fix the drive shaftto the impeller, and the second centering feature engageable with thefirst centering feature to concentrically align the impeller with thedrive shaft.
 25. The centrifugal pump of claim 24, wherein the firstcoarse thread of the impeller is a female thread and the second coarsethread of the drive shaft is a male thread.
 26. The centrifugal pump ofclaim 24, wherein the first and second coarse threads are trapezoidalthreads.
 27. The centrifugal pump of claim 24, wherein the firstcentering feature is a bore formed in the impeller and the secondcentering feature is a nubbin formed at a distal end of the drive shaft.28. The centrifugal pump of claim 27, wherein the nubbin and the borefit together with a radial clearance of less than 0.004 inches.
 29. Thecentrifugal pump of claim 24, wherein the drive shaft is part of a drivemechanism further comprising: a casing having an inlet and an outlet,the casing comprising: an inlet-side wall having an inlet apertureformed therein; an outlet-side wall joined to the inlet-side wall toform a cavity within the casing, the outlet-side wall having an outletaperture; a drive shaft housing affixed to the casing, the drive shaftrotatably received in the drive shaft housing; at least one bearingsupported by the drive shaft housing and rotatably supporting the driveshaft; a drive side wear plate connected to the drive shaft; and abiasing element between the drive side wear plate and the impeller whichbiases the drive side wear plate toward the drive shaft housing and awayfrom the impeller.
 30. The centrifugal pump of claim 29, wherein: thefirst centering feature of the drive shaft comprises a locating nubbinat a distal end thereof; the second centering feature of the impellerincludes a locating bore sized to receive the locating nubbin; the driveshaft is operably connected to the impeller by engagement of the firstcoarse thread with the second coarse thread, thereby allowing for aradial play in the drive shaft, and the drive shaft is concentricallylocated with respect to the impeller by a close-tolerance interactionbetween the locating nubbin and the locating bore such that the radialplay is eliminated.
 31. The centrifugal pump of claim 30, wherein theradial play is less than 0.004 inches.
 32. The centrifugal pump of claim29, wherein the outlet-side wall includes an outer drive aperture formedtherein, the outer drive aperture sized to receive the impeller, thecasing further comprising: a partition wall interposed between theinlet-side wall and the outlet-side wall to form an inlet pump chamberand an outlet pump chamber, the partition wall having an inner driveaperture positioned to allow fluid communication between the inlet pumpchamber and the outlet pump chamber via the inner drive aperture.
 33. Acentrifugal pump comprising: a drive mechanism; an impeller drivinglyconnected to the drive mechanism; a casing having an inlet and anoutlet, the casing comprising: an inlet-side wall having an inletaperture formed therein; an outlet-side wall joined to the inlet-sidewall to form a cavity within the casing, the outlet-side wall having anoutlet aperture; a bore extending inwardly from the exterior of theoutlet-side wall whereby the bore is accessible to a user of the pump; adrive disassembly system comprising: a guide rail sized to be snuglyreceived within the bore; and a rail guide having a bearing and a flangefixed to the bearing, the bearing sized to be slidingly received on theguide rail while the flange is fixed to the drive mechanism, such thatthe drive mechanism can be assembled into or removed from the casingwhile being supported by the guide rail.
 34. The centrifugal pump ofclaim 33, wherein the casing further comprises: a partition wallinterposed between the inlet-side wall and the outlet-side wall to forman inlet pump chamber and an outlet pump chamber, the partition wallhaving an inner drive aperture positioned to allow fluid communicationbetween the inlet pump chamber and the outlet pump chamber via the innerdrive aperture; and a stiffener extending through the outlet pumpchamber from the outlet-side wall to the partition wall, the stiffenerhaving the bore formed therein as a blind bore.
 35. The centrifugal pumpof claim 33, wherein: the drive mechanism includes a housing secured tothe casing by a plurality of first fasteners passing through acorresponding plurality of annularly arranged apertures formed in thehousing, the first fasteners threadably received in the casing; and theflange of the rail guide is secured to the casing by a plurality ofsecond fasteners threadably received in a plurality of annularlyarranged apertures formed in the flange, the plurality of annularlyarranged apertures formed in the flange of the rail guide oversizedrelative to the size of the plurality of second fasteners, wherebyalignment of the drive disassembly system relative to the casing is afunction of interaction between the guide rail and the bearing ratherthan between the flange and the casing.
 36. The centrifugal pump ofclaim 33, wherein an outer surface of the guide rail includes a notchpositioned to be adjacent the exterior of the outlet-side wall when theguide rail is fully received in the bore, the drive disassembly systemfurther comprises a rail keeper shaped to engage the notch andthereafter be secured to the casing such that the rail keeper and thecasing cooperate to axially fix the guide rail with respect to thecasing.
 37. The centrifugal pump of claim 36, wherein the drivedisassembly system further comprises a caster selectively fixed to thedrive mechanism, the caster positioned to cooperate with the guide railto support the drive mechanism while the drive mechanism is assembledinto or removed from the casing.
 38. A method of disassembling a drivemechanism from a centrifugal pump, the method comprising: inserting arail into a bore formed in a casing of the pump, such that the rail fitssnugly within the bore; sliding a rail guide over the rail and intoengagement with the pump; affixing the rail guide to the drive mechanismwhile maintaining the rail guide in sliding engagement with the rail;and disconnecting the drive mechanism from the casing and sliding thedrive mechanism away from the casing using the support of the rail. 39.The method of claim 38, further comprising affixing a caster to a lowerportion of the drive mechanism, the step of disconnecting includingrolling the caster on a support surface.
 40. The method of claim 38,further comprising reconnecting the drive mechanism to the casing usingthe support of the rail.
 41. The method of claim 38, further comprising,after the step of inserting the rail into the bore, of connecting a railkeeper to the casing, the rail keeper engaging a notch formed in therail to axially fix the rail relative to the casing.